Method of manufacturing an article by molding

ABSTRACT

A method of manufacturing a component by molding is provided. A mold has a mold surface representing a negative image of the component. The mold has openings in the mold surface. Flow channels extending from the openings in the mold surface and are connectable to a suction device. Further, the mold has a periphery delimiting the mold surface. A bag is fixed to the periphery of the mold. The bag is inflated to a pressure level above ambient pressure. The pressure is released from the bag while sucking the bag to the mold surface using the suction device. Fabrics are layered onto the bag while the bag is kept sucked to the mold surface. Resin is introduced into the fabrics and then the resin is cured.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of European Patent Application No.12159420.4 EP filed Mar. 14, 2012. All of the applications areincorporated by reference herein in their entirety.

FIELD OF INVENTION

A method of manufacturing a component by molding is provided. Morespecifically, a method of manufacturing a wind turbine rotor blade bymolding is provided.

BACKGROUND OF INVENTION

Large molded articles, like for example wind turbine rotor blades, aretypically manufactured by resin transfer molding (RTM) and, inparticular, by vacuum assisted resin transfer molding (VARTM). In suchmethods, fiber material is laid in a mold cavity and then a resin isinjected into the fiber material. In case of vacuum assisted resintransfer molding, a vacuum is applied to the mold cavity in order toassist the injection of resin into the fiber material. To allow forremoving the finished article from the mold, a release agent is providedbetween the surface of the mold cavity and the fiber material. Examplesof resin transfer molding processes are described for example in EP 1310 351 B1, WO 2006/058540 A1, WO 2006/058541 A1, and WO 2007/038930 A1.

SUMMARY OF INVENTION

It is an objective to provide a method of manufacturing a component bymolding. This objective is achieved by a method of manufacturing acomponent by molding according to the independent claim. The dependingclaims comprise further embodiments.

The method of manufacturing the component by molding includes severalsteps. A mold with a mold surface representing a negative image of thecomponent to be manufactured is provided. The mold surface comprisesopenings and flow channels extending from the openings of the moldsurface and being connectable to a suction device. Further, the mold hasa periphery delimiting the mold surface. A bag, for example a plasticbag, is attached or fixed to the periphery of the mold. The bag isinflated to a pressure level above ambient pressure, for example 5% to50% above ambient atmospheric pressure, and in particular between 10%and 20% above ambient atmospheric pressure. The pressure of the plasticbag, which is above ambient pressure, is released from the bag so thatthe bag is sucked to the mold surface using the suction device. Fabrics,or other materials, for example fiber material, are layered onto the bagwhile the bag is kept sucked to the mold surface. A resin is introducedinto the fabrics, which lay on the bag, and the resin is cured.

Sucking the plastic bag to the mold surface may continue until the resinis cured.

In a specific embodiment, the mold surface represents a negative imageof a wind turbine rotor blade.

The described method allows for providing a wrinkle-free air-tightplastic film on the mold surface forming a basis for the layering offiber material. The plastic material of the plastic bag simplifiesreleasing the finished component after the molding process without acostly and time-consuming preparation of the mold surface with a releaseagent. At the same time, the plastic bag forms a replaceable plasticvacuum membrane on the mold surface. Such a membrane allows a highquality surface finish of the molded component. Moreover, when themolded article is finished, the membrane formed by the plastic bag maystay on the mold surface of the component so as to protect the surfaceduring transportation. The plastic bag may then be removed on site aftertransportation.

In another embodiment, the flow channels are connectable to a pump orblower and a fluid, for example air, is pumped or blown through the flowchannels to the openings in the mold surface when the plastic bag isbeing laid onto the mold surface. The fluid then forms a fluid filmbetween the plastic bag and the mold surface, thus reducing friction andsimplifying attaching the plastic bag to the periphery of the moldwithout wrinkles.

When the mold surface is a concave surface, a plastic bag that isslightly smaller, for example 2% to 10% smaller, in particular 3% to 5%smaller, than the mold surface may be used. Then, at least a part orstrip of the plastic bag is heated when the bag is sucked to the moldsurface. The heat weakens the plastic in order to allow a finalexpansion leading to a whole coverage of the mold surface by the plasticbag. For example, hot air may be used for heating the plastic bag.

A suitable material for the use as plastic of the plastic bag ispolycarbonate. This material has a melting point that is high enough towithstand the exothermic reaction of the epoxy typically used in resintransfer molding. Yet, the melting point is low enough to allow a finalexpansion leading to a whole coverage of the mold surface by simplyheating the plastic with hot air. Hence, in an embodiment, apolycarbonate bag is used as plastic bag.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a part of a mold for a wind turbine rotorblade in a top view.

FIG. 2 schematically shows a first step of the method in a sectionalview through the mold of FIG. 1.

FIG. 3 schematically shows a further step of the method in a sectionalview through the mold part of FIG. 1.

FIG. 4 schematically shows a still further step of the method in asectional view through the mold part of FIG. 1.

FIG. 5 schematically shows a still further step of the method in asectional view through the mold part of FIG. 1.

DETAILED DESCRIPTION OF INVENTION

The figures show a mold part that is used for forming a wind turbinerotor blade as an example for a component to be manufactured by resintransfer molding. The mold part shown in the figures is the mold partfor forming a suction side of the blade. In principle, the blade may beformed by separately forming the shells of the suction side and thepressure side of the blade and then combining both shells to establishthe wind turbine rotor blade. On the other hand, it is also possible toform the whole shell in a single molding step if the mold part forforming the pressure side (not shown) and the mold part for forming thesuction side are designed such that they may be combined to form aclosed molding space and if a mold core is present.

The mold part 1 (only referred to as mold in the following) shown in thefigures comprises a mold surface 3 which is a negative impression of thesuction side to be formed (see FIG. 2). Hence, the mold surface has aconcave shape. The mold surface 3 is delimited by a periphery 5 whichcomprises means for fixing a plastic bag 13 thereto. The means may be,for example, an adhesive, clamps, pins, etc. Furthermore, the moldsurface comprises a plurality of openings 7 (see FIG. 2) by which afluid, in particular air, may be sucked from the area above the moldsurface or blown into this area. To allow for sucking or blowing, theopenings 7 are connectable to a suction device or a blowing device viaflow channels 9 which connect the openings 7 to the suction device orblowing device. In the present embodiment, there is a combined suctionand blowing device 11, for example a pump or a fan which allowsreversing the flow direction. The mold may, for example, be created fromaluminum profiles, for example in a milling process.

In the following, the method will be described with respect to FIGS. 2to 5 which schematically show steps of the method in form of sectionalviews through the mold 1 of FIG. 1.

In a first step of the method, a plastic bag 13 is fixed to theperiphery 5 of the mold 1. The dimension of the plastic bag 13 isslightly smaller than the dimension of the mold 1 so that the plasticbag 13 is not contact with the concave mold surface 3, at least in thecentral part of the mold surface 3. The mold 1 with the plastic bag 13affixed to the periphery 5 of the mold is shown in FIG. 2.

Putting the plastic bag 13 into the mold 1 may be done for example byunrolling the bag 13 roughly to the correct position and then blowingair out of the openings 7 of the mold surface 3 to reduce friction inthe plastic which allows fixing the edges of the plastic bag 13 to theperiphery 5 without producing wrinkles in the plastic bag 13.

Once the edges of the plastic bag 13 are fixed to the periphery 5 of themold 1, the bag 13 is slightly inflated to remove any uneven tension inthe plastic. The inflated bag 13 is shown in FIG. 3.

Once the plastic bag 13 has adapted the correct shape, the pressure thatis used for slightly inflating the plastic bag 13 is released and air isslowly sucked out of the space 17 between the plastic 13 and the moldsurface 3 by use of the combined suction and blowing device 11. In otherwords, while the pressure is released vacuum is slowly applied to thespace 17 between the bag 13 and the mold surface 3. Thereby, the plasticbag 13 will settle without wrinkles, because the bag 13 is slightlysmaller than the convex surface to be covered. The section 15 of themold surface which defines the root end of the wind turbine rotor bladeto be formed (compare FIG. 1) may be slightly extended avoiding sharpangles to allow the plastic bag 13 to adapt the correct shape withoutwrinkles.

Since the plastic bag 13 is slightly smaller than the surface 3 to becovered, the bag 13 needs to be expanded in order to rest against themold surface 3. In order to simplify expansion of the bag 13, theplastic bag 13 may be heated, at least in a central strip in order toweaken the plastic thus reducing resistance against expansion of theplastic bag 13. In the present embodiment, the heating is done by a hotair blower 19 that is moved over the plastic bag 13 in the mold 1 andheats at least a central strip of the plastic bag 13. However, othermeans/devices of heating the plastic bag 13, like infrared lamps,filaments, etc. may be used instead of a hot air blower 19.

The weakened plastic then allows a final expansion of the plastic bag 13to bring it to rest against the mold surface 3. The final expansion ofthe plastic bag 13 by weakening the plastic by the hot air blower 19 isschematically shown in FIG. 4. A suitable plastic material forperforming this expansion process is polycarbonate which has the correcttemperature resistance for the practical application since the meltingpoint is high enough the withstand the temperatures during the curing ofthe resin in the molding process, and the melting point of which is yetlow enough that it may be weakened for expansion by use of hot air. Forthe weakened plastic, the suction provided by the combined suction andblowing device 11 is strong enough to suck the plastic against the moldsurface 3.

Once the plastic bag 13 rests against the whole mold surface, as shownin FIG. 5, layering of fiber material may begin. After the fibermaterial has been laid into the mold 1, the mold is closed by a secondmold part or an air tight cover like a vacuum bag and resin isintroduced into the fiber material. Introducing the resin into the fibermaterial may be assisted by applying a vacuum to the space accommodatingthe fiber material.

After the fiber material is impregnated by the liquid resin, heat isapplied for curing the resin in order to manufacture the shell of thewind turbine rotor blade. After the curing is complete, the vacuumsucking the plastic bag 13 to the mold surface 3 is released. Theplastic bag 13 then allows removing the finished wind turbine rotorblade shell from the mold 1 easily. In addition, removing the shell maybe further assisted by blowing air through the openings 7 of the moldsurface 3. The plastic bag 13 may be kept at the outside of the windturbine rotor blade during transportation so as to protect the surfaceof the rotor blade. The bag 13 would then be removed on the constructionsite after transportation.

The described method allows a simple and easy removal of the finishedwind turbine rotor blade shell from the mold without the use of arelease agent. Moreover, using the plastic bag 13 provides a highquality surface finish of the shell since the plastic bag 13 covers themold surface without wrinkles. Putting the plastic bag 13 onto the moldsurface without wrinkles may be achieved by reducing friction by blowingair out of the openings 7 of the mold surface 3. Inflation of theplastic bag 13 then removes unevenly distributed tension in the plasticbag 13. By sucking the plastic bag 13 towards the mold surface 3, whilereleasing the pressure out of the inflated plastic bag, leaves the bag13 in tension while it settles towards the mold surface 3 which preventsfrom a formation of wrinkles in the plastic bag 13. The remainingtension is then removed by the hot air blower 19 or any other suitableheating device to soften the plastic so that the plastic may settlecompletely to the mold surface 3.

Although the present invention has been described with respect to aspecific embodiment in conjunction with the accompanying drawingsdeviations from this embodiment are possible. For example, while in thepresent embodiment the heating of the plastic bag is done from the sideof the bag which shows away from the mold surface, the heating could aswell be done from the mold surface. Moreover, although polycarbonate ismentioned as material of the bag, any other material which is suitableto withstand the temperatures during curing of the resin and which maybe sufficiently softened for the final expansion process may be used asmaterial for the plastic bag. Softening does not necessarily need to beperformed by heating. It could as well be done by, for example, chemicalmeans. Hence, the present invention shall not be restricted to theexemplary embodiment but shall only be delimited by the appended claims.

We claim:
 1. A method of manufacturing a component by molding,comprising: providing a mold with a mold surface, wherein the moldrepresents a negative image of a component to be manufactured, whereinthe mold comprises openings in the mold surface, flow channels extendingfrom the openings and being connectable to a suction device, and aperiphery delimiting the mold surface; attaching a bag to the peripheryof the mold; inflating the bag to a pressure level above ambientpressure; releasing the pressure from the bag while sucking the bag tothe mold surface using the suction device; layering fabrics onto the bagwhile the bag is kept sucked to the mold surface; and introducing aresin into the fabrics and curing the resin.
 2. The method as claimed inclaim 1, wherein the flow channels are connectable to a pump or blowerand a fluid is pumped or blown through the flow channels to the openingsof the mold surface when the bag is being laid onto the mold surface. 3.The method as claimed in claim 1, wherein the mold surface is a concavesurface, wherein the bag is slightly smaller than the mold surface, andwherein at least a strip of the bag is heated when the bag is sucked tothe mold surface.
 4. The method as claimed in claim 3, wherein hot airis used for heating the bag.
 5. The method as claimed in claim 1,wherein the bag is sucked to the mold surface until the resin is cured.6. The method as claimed in claim 1, wherein the bag comprisespolycarbonate.
 7. The method as claimed in claim 1, wherein the moldsurface represents a negative image of a wind turbine rotor blade.